This invention relates to primers to enhance bonding of materials to metal substrates.
A number of special problems are encountered when attempting to bond materials to a metal substrate. A primary problem is that many desirable hot melt applied coatings, sealants, and adhesives do not adhere well to metal because the hot melt sets up before it can fully adhere or "wet out" the surface of the metal. The application of adhesives and sealants to metals from a hot melt is thus hampered by the tendency of metals to be good conductors of heat. In certain specialized areas, such as double glazed windows where a metal frame with a preapplied elastomeric sealant is sandwiched between two panes of glass and heated, the operation is further complicated by the necessity to keep the temperature relatively low to prevent volatiles from being released which would fog the glass. The difficulty cannot be overcome simply by using a less viscous sealant. A certain minimum thickness of sealant is required to maintain proper dimensions and seal flexibility; a low viscosity sealant would be squeezed out. Finally, the final seal must exhibit sufficient resistance to shearing forces to maintain the integrity of the finished window unit.